Electrosurgical device and methods

ABSTRACT

An electrosurgical probe with internal cooling for use in systems and methods for lesioning in bone and other tissue is disclosed. The probe includes a distal electrical insulator, a proximal electrical insulator, a distal electrical conductor defining a distal electrode with a closed distal end and a proximal electrical conductor defining a proximal electrode, the distal electrode longitudinally spaced apart and electrically isolated from the proximal electrode by the distal electrical insulator. The distal electrode has a closed proximal end formed by a distal face of the distal electrical insulator to thereby define a closed distal inner lumen for circulating the cooling fluid. The proximal electrode has a closed distal end formed by a proximal face of the distal electrical insulator and a closed proximal end formed by a distal face of the proximal electrical insulator to thereby define a closed proximal inner lumen for circulating the cooling fluid.

The present application is a continuation of U.S. Ser. No. 16/660,067,filed Oct. 22, 2019, which is a continuation of U.S. application Ser.No. 15/782,229, filed Oct. 12, 2017 (U.S. Pat. No. 10,448,990); which isa continuation of U.S. application Ser. No. 14/928,568, filed Oct. 30,2015 (U.S. Pat. No. 9,788,889); which is a divisional of U.S.application Ser. No. 13/643,310, filed Oct. 25, 2012 (U.S. Pat. No.9,173,700); which is a U.S. 371 national stage of InternationalApplication No. PCT/CA11/50203, filed Apr. 15, 2011; which claims thebenefit of U.S. Provisional Application No. 61/328,118, filed Apr. 26,2010; all of which are incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to an electrosurgical device. More specifically,the disclosure relates to an electrosurgical probe and methods of usethereof.

BACKGROUND

US application 20070016185 to Tullis et al is for an electrosurgicalsystem. It discloses an electrode assembly for lesioning that includesan electrode surrounded by layers of insulation and tubing but does notdisclose cooling of the lesioning electrode.

Desinger et al (US 2004/0167517) discloses a probe having two distalregion electrodes with the distal electrode tip having a cone shape thatextends distally. Fluid in the lumen of the probe is spaced apart fromthe furthest point of the distal tip electrode.

Fay et al (US 2009/0156981) discloses a flexible catheter having aplastic tip and a plastic shaft tube with electrodes attached to it.

Some prior art bi-polar probes, such as those described in USapplication 2004/0167517 to Desinger et al and in US application2009/0156981 to Fay et al, have configurations that allow cooling fluidto contact both the active electrode and the return electrode. Ascooling fluid often has some conductivity, the flow of coolant betweenthe electrodes will cause some energy to be transmitted within the proberather than to surrounding tissue, resulting in a loss of effectivenessand possible safety concerns. The stray energy can also affect impedancemeasurements, causing further problems for devices that measureimpedance.

SUMMARY

A bipolar probe used for lesioning in tissue can be cooled by includingtubular electrodes configured such that the inner surface of eachelectrode is cooled while keeping the electrodes electrically isolated.By providing such a probe the coolant is contained in a volume that iselectrically isolated from at least one of the electrodes whereby thefluid does not form a conductive link between the electrodes. The probecan include a means for temperature monitoring, which may beparticularly useful when used in tissue that hinders the predictabilityof lesioning, such as electrically insulative tissue.

Thus, for example, embodiments of the present invention include anelectrosurgical probe comprising at least two electrically isolatedconductors and a lumen for circulating a cooling fluid within only oneof said at least two electrically isolated conductors, such that onlyone of the conductors is directly cooled by the cooling fluid. Thecooling fluid circulating within the one conductor nonetheless functionsto reduce the temperature of the at least two electrically isolatedconductors.

In a first broad aspect, embodiments of the present invention are for anelectrosurgical probe comprising the following: at least twoelectrically isolated electrical conductors, including an innerelectrical conductor and an outer electrical conductor. The innerelectrical conductor defines a lumen for the circulation of a coolingfluid therein. An inner electrical insulator disposed between theelectrical conductors electrically isolates the electrical conductorswith the electrical insulator having sufficient thermal conductivity toallow for cooling of the at least two electrical conductors when thecooling fluid is circulating within the lumen of the inner electricalconductor. It is optional that the inner electrical insulator has athickness of about 0.0254 mm (0.001″).

Some embodiments of the first broad aspect include an outer electricalinsulator disposed on the outer electrical conductor, the outer andinner electrical conductors being elongated, the inner electricalconductor being disposed coaxially within the outer conductor, and theinner conductor having a closed distal end.

The first broad aspect also includes embodiments wherein a distalportion of the inner conductor is exposed to define a distal electrode,and a distal portion of the outer conductor is exposed to define aproximal electrode.

Some embodiments further comprise a first temperature sensor that isproximate the distal electrode or is positioned at or adjacent to thedistal electrode. The first temperature sensor can protrude from asurface of the distal electrode for enhancing isolation from the coolingfluid circulating within the inner conductor lumen. Embodiments caninclude a second temperature sensor, and, in some specific embodiments,the first temperature sensor is proximate the distal electrode and thesecond temperature sensor is proximate the proximal electrode.

In some embodiments of the first broad aspect, when in use, the coolingfluid circulates within the inner electrical conductor lumen to contacta portion of an inner surface of the inner electrical conductor fordirect cooling of the inner electrical conductor. The inner electricalinsulator contacts the outer electrical conductor and the innerelectrical conductor, whereby the cooling fluid circulating within theinner electrical conductor lumen indirectly cools the outer electricalconductor. In some such embodiments, a thickness of the outer electricalconductor is substantially constant along its length and a thickness ofthe inner electrical conductor is substantially constant along itslength.

The first broad aspect also includes some embodiments wherein a surfacearea of the portion of the inner electrical conductor configured todirectly contact the cooling fluid is larger than a surface area of anouter surface of the distal electrode and an inner surface of the outerelectrical conductor that is indirectly cooled by the cooling fluid hasan area larger than an outer surface of the proximal electrode.

Some embodiments further comprise a fluid inlet tube coupled to theinner electrical conductor lumen for supplying the cooling fluid, afluid outlet tube coupled to the inner electrical conductor lumen toallow the cooling fluid to exit with the option that the fluid outlettube extend along a majority of the length of the inner electricalconductor lumen. Some embodiments have a distal end of the fluid inlettube which is proximate the proximal electrode. The fluid outlet tubecan extend along a majority of the length of the inner electricalconductor lumen.

In some embodiments of the first broad aspect, the inner electricalinsulator is exposed beyond the distal edge of the proximal electrode todefine an exposed inner electrical insulator. In some particularembodiments, the distal electrode, the exposed inner electricalinsulator, and the proximal electrode have a length ratio of about 1:1:1wherein it is possible that distal electrode has a length of about 10mm, the exposed inner electrical insulator has a length of about 10 mm,and the proximal electrode has a length of about 10 mm. In otherembodiments, the distal electrode, the exposed inner electricalinsulator, and the proximal electrode have a length ratio of about2:1:2, with the possibility that the distal electrode has a length ofabout 4 mm, the exposed inner electrical insulator has a length of about2 mm, and the proximal electrode has a length of about 4 mm. In yetother embodiments, the distal electrode, the exposed inner electricalinsulator, and the proximal electrode have a length ratio of about7:6:7, wherein the distal electrode has a length of about 7 mm, theexposed inner electrical insulator has a length of about 6 mm, and theproximal electrode has a length of about 7 mm.

In a second broad aspect, embodiments of the present invention are foran electrosurgical probe comprising the following: a distal electricalconductor defining a distal electrode with a closed distal end and aproximal electrical conductor defining a proximal electrode, with thedistal electrode longitudinally spaced apart and electrically isolatedfrom the proximal electrode by a distal electrical insulator. The distalelectrode has a closed proximal end formed by a distal face of thedistal electrical insulator to thereby define a closed distal innerlumen for circulating a cooling fluid. The proximal electrode has aclosed distal end formed by a proximal face of the distal electricalinsulator and a closed proximal end formed by a distal face of aproximal electrical insulator to thereby define a closed proximal innerlumen for circulating a cooling fluid.

In some embodiments of the second broad aspect, the probe furthercomprises a first fluid inlet tube for supplying the distal inner lumenand a first fluid outlet tube for exit of fluid therefrom, and a secondfluid inlet tube for supplying the proximal inner lumen and a secondfluid outlet tube for exit of fluid therefrom.

The second broad aspect includes some embodiments wherein the distalelectrode and the proximal electrode have substantially the samediameter. In some embodiments, the distal and proximal electricalconductors are elongated.

Some embodiments comprise a first temperature sensor located, in somespecific embodiments, proximate the distal electrode or, in alternateembodiments, positioned at or adjacent to the distal electrode. Thefirst temperature sensor can protrude from a surface of the distalelectrode for enhancing isolation from the cooling fluid circulatingwithin the distal inner lumen.

Probes of the second aspect can further comprise a second temperaturesensor, and, in some specific embodiments, the first temperature sensoris proximate the distal electrode and the second temperature sensor isproximate the proximal electrode.

In some embodiments of the second broad aspect, when the probe is inuse, the cooling fluid circulating within the distal inner lumencontacts a portion of an inner surface of the distal electricalconductor for direct cooling of the distal electrical conductor and thecooling fluid circulating within the proximal inner lumen contacts aportion of an inner surface of the proximal electrical conductor fordirect cooling of the proximal electrical conductor.

In some embodiments, a thickness of the proximal electrical conductor issubstantially constant along its length, and, alternatively or inaddition, a thickness of the distal electrical conductor is alsosubstantially constant along its length.

In some embodiments of the second broad aspect the distal and theproximal electrical conductors are electrically conductive along theirlengths. Furthermore a surface area of the distal electrical conductorconfigured to directly contact the cooling fluid can be substantiallysimilar to an area of an outer surface of the distal electrode. Also, asurface area of the proximal electrical conductor configured to directlycontact the cooling fluid can be substantially similar to an area of anouter surface of the proximal electrode.

In a third broad aspect, embodiments of the present invention include asystem comprising the following: an electrosurgical generator, a sourceof cooling fluid, and at least one electrosurgical probe. Anelectrosurgical probe comprises the following: at least two electricallyisolated electrical conductors, including an inner electrical conductorand an outer electrical conductor, the inner one of the electricalconductors defining a lumen for the circulation of a cooling fluidtherein, and an inner electrical insulator disposed between the innerand outer electrical conductors for electrically isolating theelectrical conductors. The inner electrical insulator has sufficientthermal conductivity to allow for cooling of the at least two electricalconductors when the cooling fluid is circulating within the lumen of theinner electrical conductor. The probe is operable to be connected to thegenerator for delivering energy between the inner electrical conductorand the outer electrical conductor in a bipolar manner and the lumen isoperable to be connected to the source of cooling fluid for deliveringfluid for cooling the inner and outer electrical conductors.

Some embodiments of the third aspect include a distal portion of theinner electrical conductor of the probe exposed to define a distalelectrode. In some embodiments, the electrosurgical probe furthercomprises a first temperature sensor with the first temperature sensorbeing located proximate the distal electrode.

Some embodiments comprise a distal portion of the outer electricalconductor being exposed to define a proximal electrode. The at least oneelectrosurgical probe further comprises a second temperature sensor,with the second temperature sensor being proximate the proximalelectrode.

In some embodiments, the electrosurgical generator is operable todeliver radiofrequency energy.

In some embodiments of the third aspect, the electrosurgical generatorcomprises a controller for monitoring the first temperature sensor andadjusting the energy delivered based on the sensed temperature.

In a fourth broad aspect, embodiments of the present invention include amethod of lesioning in bone tissue, the method comprising the followingsteps: providing a bipolar probe having an active tip comprising atleast two electrodes for delivering energy, advancing the active tipinto a bone tissue, delivering energy between the at least twoelectrodes in a bipolar manner whereby energy is delivered to tissue,and supplying cooling fluid to the active tip for internal cooling ofthe at least two electrodes.

Some embodiments further comprise selecting a temperature for thecooling fluid that is supplied to the active tip wherein the temperatureselected for the cooling fluid can be from just above 0 degrees C. toabout 30 degrees C. Such methods can further comprise adjusting the flowrate of the cooling fluid.

Some embodiments of the fourth broad aspect include monitoring thetemperature of tissue that the energy is delivered to and, in certainembodiments, controlling the delivery of energy using the temperature ofthe tissue that the energy is delivered to.

In further embodiments of the fourth aspect, the bone is a vertebralbody, the energy is delivered to a nervous tissue generating painsignals at the bone-tumor interface, and/or the active tip is advancedthe into a trabecular bone.

Some methods according to the fourth aspect of the invention include anassembly comprising a cannula with a stylet disposed within. Theassembly is used to advance the probe into the vertebral body, and thestylet is withdrawn from the cannula subsequent to the introducerassembly being advanced into the vertebral body.

In some embodiments of the fourth broad aspect, the polarity of theenergy delivered to the at least two electrodes is reversible.

Some embodiments of the fourth aspect relating to the polarity of theprobes being reversible include methods comprising emitting astimulation pulse comprising a continuous train of biphasic waves at aset frequency, navigating the active tip through tissue, reversing thepolarity of the at least two electrodes to identify which electrode astimulated nerve is in proximity to, and repeating the previous stepsuntil the location of the nerve is determined.

Some other embodiments of the fourth aspect relating to the polarity ofthe probes being reversible include methods comprising the following:delivering energy to at least two electrodes for ablation, and reversingthe polarity of the energy to the at least two electrodes. The methodcan include each probe being active for about 50 percent of the time.

Some embodiments of the fourth aspect relating to monitoring tissuetemperature include methods comprising placing at least one externaltemperature sensor at the boundary of a desired lesion, monitoring theat least one external temperature sensor during energy delivery, anddetermining the lesion is complete when the external temperature (thetemperature from the sensor at the boundary) reaches a predefined value.

Some embodiments of the fourth broad aspect include methods wherein theenergy is delivered to a nerve within a vertebral body, wherein it isoptional that the energy is delivered to a basivertebral nerve.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be readily understood, embodiments ofthe invention are illustrated by way of examples in the accompanyingdrawings, in which:

FIG. 1 is an illustration of a probe 100 in accordance with anembodiment of the present invention;

FIG. 2a is a side view of a probe 100, showing various features intransparency for ease of illustration, in accordance with an embodimentof the present invention;

FIG. 2b is a cross-sectional view of probe 100, taken along line 2 b-2 bof FIG. 2a , in accordance with an embodiment of the present invention;

FIG. 3 is an illustration of a target location, in accordance with anembodiment of a method of the present invention;

FIGS. 4a and 4b are illustrations of a method in accordance with anembodiment of the present invention;

FIG. 5 is an illustration of a probe 100, in accordance with analternate embodiment of the present invention; and

FIGS. 6a, 6b and 6c are illustrations of a portion of a probe 100, inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Creating predictable lesions in insulative tissue such as bone can beaided by using a bi-polar probe with internal cooling. Embodiments ofsuch a probe include tubular electrodes configured such that the innersurface of each electrode is cooled, directly or indirectly, whilekeeping the electrodes electrically isolated. One possible configurationis an electrosurgical probe comprising two electrically isolatedelectrical conductors with an inner one of the conductors inside of theother and the inner electrical conductor defining a lumen for thecirculation of a cooling fluid inside of it. The probe also has anelectrical insulator layer between the electrical conductors forelectrically isolating the electrical conductors. The electricalinsulator has sufficient thermal conductivity to allow for cooling ofthe outside electrical conductor by cooling fluid circulating within thelumen of the inner electrical conductor. Thus, only one conductor iscooled directly, i.e., in contact with the cooling fluid, while theother conductor is indirectly cooled.

With specific reference now to the drawings in detail, it is stressedthat the particulars shown are by way of example and for purposes ofillustrative discussion of certain embodiments of the present inventiononly. Before explaining at least one embodiment of the invention indetail, it is to be understood that the invention is not limited in itsapplication to the details of construction and the arrangement of thecomponents set forth in the following description or illustrated in thedrawings. The invention is capable of other embodiments or of beingpracticed or carried out in various ways. Also, it is to be understoodthat the phraseology and terminology employed herein is for the purposeof description and should not be regarded as limiting.

FIG. 1 is an illustration of a probe 100 in accordance with anembodiment of the present invention. The probe comprises an innerelongate conductor 30 and an outer elongate conductor 50. The inner andouter conductors 30, 50 each have a hollow tubular configuration anddefine a lumen there-through. The inner and outer conductors 30, 50 arecoupled to an energy supply at proximal ends thereof. In one example,the energy supply may comprise a radiofrequency (RF) energy deliverysource and an energy sink. In one specific example, the inner conductor30 functions as an active electrode and is coupled to an RF energydelivery source, and the outer conductor 50 is coupled to an energy sinksuch as a ground connection, forming a return electrode. In other words,the inner conductor 30 functions as a control electrode and the outerconductor 50 functions as a neutral or ground reference electrode. Inanother example, the outer conductor 50 functions as an active electrodeand the inner conductor 30 functions as a return electrode. In suchembodiments, probe 100 can be operated in a bipolar manner, where energyis delivered substantially between conductors 30, 50. The inner andouter conductors 30, 50 may be connected to the RF energy deliverysource and ground via an electrical connection through a probe handle 8,shown in FIG. 2a , which may be coupled to a proximal end of probe 100.The inner conductor 30 is disposed coaxially within the lumen of theouter conductor 50. The inner and the outer conductors 30, 50 eachcomprise an electrically conductive portion at least along a lengththereof and more specifically, at least along a distal segment ofconductors 30, 50. Each of the electrically conductive portions iscoupled to an energy supply through an electrically conductive pathway.

In FIG. 1, the inner conductor 30 and the outer conductor 50 areelectrically conductive along their length. In one example as shown inFIG. 1, the inner conductor 30 has a length S1, and the outer conductor50 has a length S2. In one example, the inner and the outer conductors30, 50 each comprise a stainless steel hypotube. In another example, theinner and outer conductors 30, 50 may comprise an electricallyconductive, biocompatible material such as titanium or nitinol. Theinner conductor 30 is electrically isolated from the outer conductor 50by an inner insulator 40 disposed between the inner conductor 30 and theouter conductor 50. In some embodiments, the inner insulator 40 extendslongitudinally along at least the entire length of the outer conductor50. In some embodiments, it has a length that is greater than the lengthof the outer conductor 50. In one example, as shown in FIG. 1, the innerinsulator has a length S3 that is greater than length S2 of the outerconductor 50. In some embodiments, the inner insulator 40 iselectrically insulative and thermally conductive. In the illustratedembodiments, the distal most portion of the inner conductor 30 isexposed at the distal tip thereof and forms a distal electrode 32 havinga length L1.

The inner elongate conductor 30 as shown in FIG. 1 and FIG. 2b has aclosed distal end and defines a lumen 34 there-through for circulating acooling fluid. The term “circulate” relates to fluid that mostly movesor is caused to move through a generally closed system in a controlledmanner rather than fluid that enters and mostly passes through thesystem to the outside environment, such as passing through an open endedtube. A fluid inlet tube 21 may be disposed within the lumen 34 tosupply cooling fluid within the inner lumen 34 from a cooling supply(not shown). A fluid outlet tube 22 may be disposed alongside the fluidinlet tube 21 within the inner lumen 34 to allow the cooling fluid toexit via a proximal end of the probe 100. The fluid outlet tube 22 mayextend along a majority of the length of the inner conductor 30. In someembodiments, fluid outlet tube 22 may be shorter than fluid inlet tube21. The outer conductor 50 has an electrical insulator 60 disposed on anouter surface thereof, along at least a portion of the outer conductor50, whereas a distal portion of the outer conductor 50 remainselectrically exposed, forming a proximal electrode 52 with a length L3.In one example, the outer insulator 60 has a length S4 as shown inFIG. 1. In one embodiment the outer insulator 60 may have a length thatis substantially the same as the length of the outer conductor 50. Theinner insulator 40 is exposed between the distal edge of the proximalelectrode 52 and the proximal tip of the distal electrode 32. The lengthof the exposed insulator is labelled as L2. The region of the probeextending from the proximal electrode 52 to the distal electrode 32forms an active tip 70. A radiopaque band 72 may be positioned at aproximal end of the active tip 70 as shown in FIG. 2a . The radiopaqueband 72 may act as a navigational reference to guide and facilitatepositioning the active tip 70 at a target location within a patient'sbody. In other embodiments, the radiopaque band may be positioned at anylocation along the active tip 70 or at any location along the probe 100.In still another embodiment, more than one radiopaque band 72 or aradiopaque marker may be positioned along the probe. In one example theradiopaque band 72 may function as a navigational reference underfluoroscopic imaging.

In one example, the proximal electrode 52 is a return electrode and thecooling fluid cools the proximal electrode 52 prior to reaching andcooling the distal electrode 32, which is the active electrode. This mayprovide a more uniform lesion to be produced when RF energy is suppliedto the probe 100. The structure of the probe 100, in one example, allowscooling fluid to indirectly cool the proximal electrode 52 and todirectly cool the distal electrode 32. The cooling fluid flows throughthe inner lumen 34 of the inner conductor 30 and cooling is transmittedindirectly to the proximal electrode 52 through thermal conductivitythrough a wall of the inner conductor 30 and a wall of the innerinsulator 40. Cooling fluid is supplied from the fluid inlet tube 21which exits into the lumen 34 near the location of the proximalelectrode 52. The relatively low temperature of the cooling fluid coolsproximal electrode 52 indirectly, thus raising the temperature of thefluid. In other words, the cooling fluid allows heat to be removed fromthe proximal electrode 52. The fluid then flows within the lumen 34 tothe distal electrode 32 at the slightly elevated temperature. Thus,cooling fluid at a lower temperature is used to indirectly cool theproximal electrode 52, whereas, cooling fluid that is at a slightlyhigher temperature passes through the distal electrode 32 to cool itdirectly. It is possible that by cooling proximal electrode 52indirectly at a lower temperature and cooling the distal electrode 32directly at a slightly higher temperature, cooling of electrodes 32, 52will be substantially equivalent. This arrangement may allow cooling tobe transmitted uniformly to both the proximal and distal electrodes 32,52, thus allowing a relatively uniform heat distribution around the twoelectrodes, which may allow a more uniform lesion to be produced whenthe electrodes 32, 52 are placed in target tissue. Providing coolerfluid to cool the proximal electrode 52 may offset the difference incooling at the proximal and distal electrodes 32, 52 due to direct andindirect cooling respectively.

In the case of the embodiment of FIG. 1, another factor that can helpcompensate for distal electrode 32 being directly cooled while proximalelectrode 52 is indirectly cooled is that proximal electrode 52 has alarger diameter and circumference. Consequently, for distal and proximalelectrodes of equal length, proximal electrode 52 will have a slightlylarger inner surface, which will increase the effectiveness of theinternal cooling fluid.

In one example, the cooling fluid may comprise water. In anotherexample, the cooling fluid may comprise saline. In an alternate examplean alcohol may be used. As a further example, an isopropyl alcohol maybe used. In one embodiment, the temperature of the cooling fluid mayrange from about its freezing point to about room temperature. In oneembodiment, the fluid inlet and outlet tubes 21, 22 may be constructedfrom a metal. In one example the fluid inlet and outlet tubes are madefrom stainless steel hypotubes and may be connected to the fluid supplyat proximal ends thereof with non-conductive supply tubes 12, 14. Thesemay comprise any non-conductive material such as a polymer. In onespecific example, the supply tubes 12, 14 comprise polyvinylchloride(PVC) tubing that may be UV (ultraviolet) glued to the stainless steelinlet and outlet tubes 21, 22. In other embodiments, any other means canbe used to join the supply tubes to the outlet tubes. In otherembodiments the fluid inlet and outlet tubes 21, 22 may be constructedfrom a non-conductive material such as a polymer. In still otherembodiments, the fluid inlet and outlet tubes 21, 22 may be formed ofalternate materials. The fluid inlet and outlet tubes 21 and 22 may bepositioned alongside each other within the lumen 34 of the innerconductor 30. In other embodiments any flow pathway may be provided tothe probe 100 to allow fluid to enter and exit the inner conductor 30.The flow pathway may comprise a fluid inflow path that is separate froma fluid outflow path which provides directional flow. In someembodiments cooling fluid may be directed into the inner conductor 30directly without use of the fluid inlet tube 21.

In one embodiment the active tip 70 may have a length (L1+L2+L3) thatranges from about 5 mm to about 40 mm. In one example, the length of thedistal electrode 32 (L1), the exposed inner insulator 40 (L2), and theproximal electrode 52 (L3) may vary in about a 2:1:2 ratio. In otherembodiments the ratio may be in about a 1:1:1 configuration. Alternateembodiments are possible as well. In other embodiments, the lengths L1,L2 and L3 may have a different ratio. In another example, the L1:L2:L3ratio is about 7:6:7.

In another embodiment, the inner and outer conductors 30, 50 may onlyextend along a portion of the probe 100. In one example inner and outerconductors 30, 50 may be electrically conductive along their lengths andmay form the proximal and the distal electrodes, 32 and 52. In onespecific example, as shown in FIG. 5, only the exposed portions of theinner and outer conductors 30 and 50 are electrically conductive, andthe inner and outer conductors 30, 50 may have substantially the samewidth. The inner and outer conductors may be spaced apart andelectrically isolated from each other by an inner insulator 40. In oneexample the inner insulator 40 may comprise a polymer. In a specificexample, the insulator 40 may comprise a substantially rigid plasticinsert. In one example the electrically isolated distal and proximalelectrodes 32 and 52 may be cooled through separate cooling sources. Asshown in FIG. 5, the distal electrode 32 is supplied with a coolingfluid through fluid inlet and outlet tubes 21 a and 22 a. Whereas,cooling to the proximal electrode 52 is supplied through cooling inletand outlet tubes 21 b and 22 b. The fluid inlet and outlet tubes maycomprise a non-conductive material such as a polymer. Each of theproximal and distal electrodes 32, 52 are coupled to an energy supplythrough electrically conductive insulated wires 94.

In this example, the distal and proximal electrodes 32 and 52 eachdefine a closed inner lumen, 34 and 54 respectively, within whichcooling fluid flows. The distal electrode 32 has a closed distal end anda closed proximal end formed by co-operative engagement of the distalelectrode proximal portion with a distal face 43 of the inner insulator40, defining the closed inner lumen 34. The proximal electrode 52 has aclosed distal end formed by co-operative engagement of the proximalelectrode distal end with the proximal face 45 of the inner insulator40, as shown in FIG. 5. The proximal electrode 52 further has a closedproximal end defined by co-operative engagement of the proximalelectrode proximal end with a distal face 65 of the outer insulator 60,defining the closed inner lumen 54. The cooling fluid is restrictedwithin the lumens 34 and 54. The distal face 65 of the outer insulator,as well as the distal 43 and the proximal face 45 of the innerinsulator, extend substantially transversally along the width of theprobe. The distal face 65 may comprise openings to allow fluid inlettubes 21 a, 21 b and fluid outlet tubes 22 a, 22 b as well as insulatedwires 94 to extend therethrough. Similarly, distal and proximal faces 43and 45 may provide openings therethrough to allow passage of the inletand outlet tubes 21 a and 21 b respectively and one of the insulatedwires 94. A seal may be provided around the openings to ensure thatcooling fluid is restricted within the lumens 34 and 54.

Additionally, a temperature sensor 80 may be positioned at a locationalong the probe 100 as shown in FIGS. 1, 2 and 5. In one embodiment thetemperature sensor 80 may be positioned substantially adjacent thedistal tip 102 of the probe 100. For example, the temperature sensor 80may protrude from the surface of the distal electrode 32. In otherwords, temperature sensor 80 may jut out or stick out from a surroundingsurface of the probe 100. In other embodiments the temperature sensor 80may be positioned at any location along the length of the probe. In someembodiments the temperature sensor 80 may be positioned at or adjacentto the active tip 70. In one example, the temperature sensor 80 maycomprise a thermocouple. In one specific example, a thermocouple may beformed using a hypotube 84 disposed within the lumen 34 of the innerconductor 30. A constantan wire can be disposed within the thermocouplehypotube 84 to form a thermocouple junction 83 about the distal tip 102,as shown in FIG. 2a . In other embodiments, a thermocouple may be formedusing a pair of wires to form a junction. In one example, a thermocoupleis positioned at a distal face of the outer electrode 52. In anotherexample, a thermocouple is positioned between the outer electrode 52 andinner insulator 40. In one example, the temperature sensor 80 is coupledto and in communication with a controller for the energy supply, such asan energy supply having an RF energy delivery source. In one example,the temperature sensor 80 may be coupled to a controller at its proximalend via the handle 8.

In some embodiments a second temperature sensor is proximate to proximalelectrode 52 and is in communication with a controller for the energysupply for providing additional information. Such an embodiment could beused with a generator capable of monitoring two temperature sensors atone time. Alternatively, a generator capable of monitoring only onetemperature at a time could be used if an external device switchedbetween the two (or more) temperature sensors.

Generally, embodiments of the present invention may comprise a pluralityof temperature sensors, which may be positioned at different locationson the probe, for example, on or adjacent to the surface of theelectrodes, between the electrodes, or at or near the electrodes,proximally or distally. A generator used in a system with two or moretemperature sensors would include an algorithm for controlling theoutput of energy based on multiple temperature readings.

The inner conductor 30 has a closed distal end. As shown in FIGS. 6a, 6band 6c , in one embodiment, the distal end of the inner conductor 30 isswaged to form a concentrically tapered end 36 with an opening 38therethrough. The size or diameter of the opening 38 is smaller than adiameter of the inner conductor 30 along its length as shown in FIG. 6c. The opening 38 allows the thermocouple hypotube 84 to extend orprotrude from the distal end face of the inner conductor 30. In someembodiments, the thermocouple hypotube 84 may be laser welded to theinner conductor 30 at a wall of the opening 38. In other examples anyother means of attachment may be used. In some embodiments where thethermocouple may be positioned at any other location along the probe,the distal end of the inner conductor 30 may be swaged in a similarmanner as disclosed above to reduce the size of the opening at thedistal end of the inner conductor hypotube 30. The reduced diameteropening may then be closed by laser welding at the distal most end. Theclosed distal end of the inner conductor 30 may be formed using othermeans. In some embodiments the closed distal end of the hypotube maycomprise a separate end piece or end cap that may be attached to thedistal end of the hypotube. In some examples, the end piece may be domeshaped, triangular shaped or may have a flat surface. The end piece mayor may not be metal. In other embodiments a closed distal end of theinner conductor may be formed by providing an end piece in the form of ametal insert which may be laser welded to the hypotube distal end. Inother embodiments, any other attachment means may be used. In oneexample, an adhesive may be used to attach the end piece to the hypotubedistal end. In one such example, the adhesive may be an ultraviolet (UV)glue.

In some embodiments, the probe size may range from an outer diameter ofabout 13 Gauge, 2.413 mm (0.095″), to about 17 Gauge, 1.47 mm (0.058″).In one example, the probe 100 has a diameter of about 17 Gauge and hasan outer conductor 50 with a length of about 215.9 mm (8.5″) and aninner conductor 30 with a length of about 228.6 mm (9.0″). The fluidoutlet tube 22 has a length of about 241.3 mm (9.5″) and extends intothe handle, whereas the fluid inlet tube 21 is about 38.1 mm (1.5″) inlength and positioned at the proximal end of the inner conductor 30. Thethermocouple hypotube 84 is positioned within the inner lumen 34 ofinner conductor 30 and has a length of about 254 mm (10″).

In one example the insulators 40 and 60 may comprise a polyester. Theinsulators 40 and 60 may be disposed onto the conductors 30 and 50,respectively, using a heat-shrink procedure. The conductors 30 and 50may be electrically conductive along their length. In one example, thepolyester is a Polyethylene terephthalate (PET). In other embodiments apolyamide, Fluorinated ethylene propylene (FEP) orpolytetrafluoroethylene (PTFE), may be used to form one or both of theinsulators 40, 60. In one embodiment the insulators 40 or 60 may beprovided in the form of a coating or a layer. In still other embodimentsPEEK may be used. In one example the thickness of the inner insulator 40may vary from about 0.0127 mm (0.0005″) to about 0.254 mm (0.010″). Thethickness of the inner insulator 40 provides sufficient thermalconductivity to allow cooling to be conveyed to the outer conductor 50.This feature allows heat to be removed from the outer conductor 50,which may allow a larger lesion to be produced and minimize charring oftissue. In one specific example, PET is used in insulators 40 and 60,each having a width of about 0.03175 mm (0.00125″).

In one embodiment of a method aspect of the present invention, the probe100 is used to treat a region within a patient's body. In oneembodiment, the region may comprise tissue with varying composition. Inone such embodiment, the tissue may comprise any one of or a combinationof vascular tissue, soft tissue, trabecular bone tissue, cortical bonetissue, fatty tissue, tumor or nervous tissue.

In one specific embodiment the probe 100 is placed within a vertebralbody. For example, as shown in FIG. 3, the probe 100 may be positionedadjacent a tumor 93 within a vertebral body at a bone-tumor interface194. The probe 100 may be used to destroy nervous tissue generating painsignals at the bone-tumor interface. In one example, the probe 100 isadvanced into a vertebral body 92 until the distal end 102 of the probeis positioned at the tumor-nerve interface at the edge of the tumor 93adjacent nerves 294, as shown in FIG. 3. In one specific example, theprobe active tip 70 may be positioned within the trabecular bone 95within the vertebral body 92 that is encased by the electricallyinsulative cortical bone 97. In one embodiment, the probe 100 ispositioned substantially adjacent the rich nerve supply within thevertebral body. In one embodiment, the probe 100 may be positionedwithin or substantially adjacent to the vertebral body in proximity tosensitive structures such as the cortical bone that may benon-conductive, or in other words, may have a low electricalconductivity.

Nerve stimulation can be used to position a probe. In bipolar nervestimulation applications, the stimulation effects are not symmetricabout each electrode. One electrode will have a larger stimulationcapacity for a given biphasic wave. The electrode that is closest to astimulated nerve can be identified by reversing the polarity of thebipolar probe, also called manipulating. Balanced stimulation of nervescan be achieved by alternating the polarity in a balanced manner. Forexample, 10 pulses could be delivered with a first electrode as thecontrol electrode to more intensely stimulate the nerves nearest to it,and then 10 pulses could be delivered with a second electrode as thecontrol electrode. An embodiment of a method using such a procedure tohelp position a probe includes the following steps: emitting astimulation pulse comprising a continuous train of biphasic waves at aset frequency, navigating the active tip through tissue, and reversingthe polarity of the two electrodes to identify which electrode astimulated nerve is closest to.

The probe 100 may improve heating capability in the vicinity of anon-conductive structure. The probe 100 provides energy in a bipolarmanner and may be used in the vicinity of a cortical bone structure orother non-conductive structures to provide treatment to thenon-conductive structure through indirect thermal conduction. Thus,probe 100 may be used to treat structures that are non-conductive inmonopolar RF applications, where the energy transmission to a ground maybe limited as the non-conductive structure is encountered in the energypathway to the ground.

In another example, probe 100 may be used to target nerves at otherlocations within the vertebral body. In still another example, the probe100 may be positioned substantially adjacent to or in the vicinity ofany other bone tissue. In yet another example probe 100 may be used totreat a highly vascular tissue such as liver. In some embodiments, theprobe 100 may be used to provide uniform or consistent lesions in thevicinity of bone or variable tissue. In other words, the probe 100 maybe used to provide lesions that are substantially homogeneous.

In one particular embodiment, an introducer needle assembly may beinserted and advanced to a target location within a patient's body. Theintroducer needle assembly may comprise a cannula with a stylet disposedtherein. In one example, the target location is a vertebral body asshown in FIGS. 4a and 4b . In such an embodiment, the introducerassembly 4 may be inserted into the vertebral body using atranspedicular approach. The introducer needle assembly may be insertedthrough the pedicle at an angle of about 15.degree. to about 25.degree.oblique to the mid-sagittal plane, which provides a trajectory to accessthe vertebral body. In another embodiment a lateral approach may beused. In still other embodiments any approach that allows access to thevertebral body may be used. As an example, any conventional approachused in standard vertebroplasty or vertebral augmentation procedures togain access to the vertebral body may be used. Once the introducerneedle assembly has been positioned at the target site, the stylet maybe withdrawn from the cannula. The probe 100 may then be insertedthrough the cannula and advanced to the target site. In someembodiments, the probe 100 can be inserted directly to the target tissueand may include a sharp trocar tip at a distal end of the probe. In onesuch example, the target tissue is a soft tissue. In another embodiment,a bilateral approach may be used to treat a vertebral body. The probe100 may be inserted into a vertebral body at a first target location tothe right of the mid-sagittal plane at an angle of about 15.degree. toabout 25.degree. to the mid-sagittal plane. A first bi-polar lesion maythen be formed at a first location within the vertebral body. The probe100 may then be inserted at a second target location to the left of themid-sagittal plane at an angle of about 15.degree. to about 25.degree.from the mid-sagittal plane. A second bi-polar lesion may then be formedat a second location within the vertebral body. In one such example, thefirst and second lesions may encompass a majority of the vertebral body.

Bipolar lesions of different geometry can be created by manipulating theduration and intensity of energy delivered through each electrode as thecontrol electrode. This is related to the higher tissue temperaturesbeing found around the control electrode. Manipulating a bipolar probecan create lesions that are peanut, mushroom or symmetric ellipsoidshaped. Keeping each electrode active for 50 percent of the time canhelp in creating symmetrical or more symmetrical lesions.

In one example, RF energy is supplied by an RF generator in a bipolarmanner to probe 100. The power output of the RF generator may betemperature controlled. In one embodiment, direct tissue temperaturemonitoring is used in conjunction with internal cooling when supplyingRF power to form a lesion. The power output may be adjusted based on themeasured temperature response of the tissue to RF heating under cooling.The temperature response of the target tissue may be monitored using thetemperature sensor 80.

One embodiment is for a system in which the user puts the selectedcoolant temperature into the system from a range from just above0.degree. C. up to about 30.degree. C. The cooling fluid is delivered bya pump unit, which is controlled by the same generator that deliversenergy. The flow rate (and correspondingly the amount of cooling) can beadjusted based on tissue characteristics and the intended lesiongeometry.

The RF energy is delivered in a bipolar manner between conductors 30 and50 and allows a lesion 90 to be formed adjacent the active tip 70. Threefactors in controlling lesion size and shape (lesion geometry) aretemperature, time of procedure, and active tip geometry which includeslength of the active tip segments and ratios of the segment lengths. Inone example the active tip 70 has a length of about 20 mm, and thedistal electrode 32, the exposed inner insulator 40, and the proximalelectrode 52 have a length ratio L1:L2:L3 of about 7:6:7. A ramp rate ofabout 10.degree. C./min is used in order to reach a set temperature ofabout 65.degree. C. to about 70.degree. C. The power is supplied forabout 15 minutes, resulting in a lesion having a size of about 30mm.times.23 mm, with a lesion volume of about 8.3 cm.sup.3.

In another example an active tip 70 with a length of about 30 mm isused, and the distal electrode 32, the exposed insulator 40, and theproximal electrode 52 have a length ratio L1:L2:L3 of about 1:1:1. Aramp rate of about 20.degree. C./min may be used. In one instance ofthis example, the ramp rate may be used to achieve a set temperature ofabout 100.degree. C. The power is supplied for about 20 minutes,resulting in a lesion size of about 45 mm.times.35 mm, with a lesionvolume of about 28.9 cm.sup.3.

In yet another example, a ramp rate of about 40.degree. C./min is usedto achieve a set temperature of about 90.degree. C. Power is applied forabout 5 minutes, resulting in a lesion size of about 15 mm.times.15 mmwith a volume of about 1.8 cm.sup.3. In some embodiments, the tissuetemperature may be maintained at between about 40.degree. C. and about100.degree. C.

In some cases, the predictability of lesioning is improved by the use ofexternal monitoring electrodes. For example, monitoring an electrode atthe periphery of a centrally-formed lesion can help a physician decidewhen to stop lesioning to ensure an adequate lesion size, or themonitoring electrode could be in communication with a generator with acontrol program that controls energy delivery. The output of a generatorcould be controlled by one or more monitoring electrodes such astemperature monitoring electrodes. One example includes placing at leastone external temperature sensor at the boundary of a desired lesion,monitoring the at least one external temperature sensor during energydelivery, and determining the lesion is complete when the externaltemperature reaches a predefined value.

In some embodiments, the power may be delivered at from about 1 Watt toabout 100 Watts. In another example power may be delivered at from about1 Watt to about 50 Watts. In other embodiments, greater than 100 Wattsof power may be delivered by the RF energy delivery source. In stillanother embodiment, less than 1 Watt of power may be delivered. In someembodiments power may be delivered for a duration of between about 2minutes to about 30 minutes. In other embodiments power may be appliedfor less than 2 minutes or greater than 30 minutes.

In some embodiments, the ramp rate may range from about 2.degree. C./minto about 100.degree. C./min. In one example, the ramp rate may be about10.degree. C./min. In another example, ramp rate may be about 20.degree.C./min. In still another example, ramp rate may be about 40.degree.C./min. In one embodiment the ramp rate may be set to optimize thetissue response to achieve the set temperature. This may preventcharring, desiccation or vaporization of tissue. In some embodiments,the power supplied to the bipolar coaxial probe 100 may be less thanpower supplied to a monopolar probe to achieve an equivalent lesion.

Thus, as described hereinabove, an electrosurgical probe with internalcooling can be particularly useful, for example, in systems and methodsfor lesioning in bone and other tissue. In some embodiments, the probeis comprised of at least two electrically isolated electrical conductorswhich are operable to deliver energy in a bipolar manner. One embodimentof such a probe includes an inner conductor inside an outer conductor.The inner electrical conductor includes a lumen for the internalcirculation of a cooling fluid. The probe also has an electricalinsulator layer between the inner and outer electrical conductors forelectrically isolating the electrical conductors. The electricalinsulator has sufficient thermal conductivity to allow for cooling ofthe outside electrical conductor by cooling fluid circulating within thelumen of the inner electrical conductor. Thus, only one conductor iscooled directly, i.e., in contact with the cooling fluid, while theother conductor is indirectly cooled. When used in a system, the probecould enable temperature monitoring to provide data for controlling thedelivery of energy through electrodes to tissue and for controlling theflow of cooling fluids to the electrodes.

The embodiments of the invention described above are intended to beexemplary only. The scope of the invention is therefore intended to belimited solely by the scope of the appended claims.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the broad scope of theappended claims. All publications, patents and patent applicationsmentioned in this specification are herein incorporated in theirentirety by reference into the specification, to the same extent as ifeach individual publication, patent or patent application wasspecifically and individually indicated to be incorporated herein byreference. In addition, citation or identification of any reference inthis application shall not be construed as an admission that suchreference is available as prior art to the present invention.

We claim:
 1. A method of lesioning in a bone of a patient using anelectrosurgical ablation probe, the method comprising: inserting atleast a portion of the electrosurgical ablation probe into the patient;positioning a distal end of the electrosurgical ablation probe adjacenta portion of the bone; supplying energy from an electrosurgicalgenerator to a first electrode positioned at the distal end of theelectrosurgical ablation probe via an inner conductor extending throughat least a portion of the electrosurgical ablation probe; deliveringenergy between the first electrode and a second electrode spaced apartfrom the first electrode, and to the portion of the bone to create alesion; electrically isolating the first electrode and the secondelectrode from one another using an insulator positioned therebetween;and circulating a cooling fluid within the electrosurgical ablationprobe to cool the first electrode and the second electrode; wherein thefirst electrode is formed from a closed distal end portion of theelectrosurgical ablation probe, and the cooling fluid is circulatedwithin at least a portion of the closed distal end portion.
 2. Themethod of claim 1, further comprising monitoring a temperature of theportion of the bone to which the energy is being delivered, andcontrolling the delivering of the energy in response to the monitoredtemperature.
 3. The method of claim 1, further comprising using anintroducer assembly to position the portion of the electrosurgical probeadjacent the portion of the bone.
 4. The method of claim 1, wherein apassageway extends through at least a portion of the electrosurgicalprobe, the passageway being configured to circulate the cooling fluid tocool at least portions of the first electrode and the second electrode.5. The method of claim 1, wherein the closed distal end portion of theelectrosurgical probe is formed at least in part by the inner conductor.6. The method of claim 1, wherein the first electrode is closer to thedistal end of the electrosurgical probe than the second electrode. 7.The method of claim 1, wherein the delivered energy is radiofrequencyenergy, and further comprising maintaining a temperature of the portionof the bone at between about 40 degrees and about 100 degrees Celsiususing the radiofrequency energy.
 8. The method of claim 7, wherein theradiofrequency energy is delivered at power levels between about 1 Wattand about 50 Watts.
 9. The method of claim 7, wherein the radiofrequencyenergy is delivered for between about 2 minutes to about 30 minutes. 10.The method of claim 7, wherein the radiofrequency energy is deliveredsuch that a temperature of the portion of the bone increases at a ramprate from about 10 degree C./min to about 80 degree C./min.
 11. A methodof lesioning in a bone of a patient using an electrosurgical ablationprobe, the method comprising: positioning an introducer assembly intothe patient; inserting at least a portion of the electrosurgicalablation probe through the introducer assembly and into the patient;positioning a distal end of the electrosurgical ablation probe adjacenta portion of the bone; supplying energy from an electrosurgicalgenerator to a first electrode positioned at the distal end of theelectrosurgical ablation probe via an inner conductor; delivering energybetween the first electrode and a second electrode spaced apart from thefirst electrode, and to the portion of the bone to create a lesion;electrically isolating the first electrode and the second electrode fromone another using an insulator positioned therebetween; and circulatinga cooling fluid within the electrosurgical ablation probe to cool thefirst electrode and the second electrode; wherein the first electrode isformed from a closed distal end portion of the electrosurgical ablationprobe, and the cooling fluid is circulated within at least a portion ofthe closed distal end portion.
 12. The method of claim 11, furthercomprising monitoring a temperature of the portion of the bone to whichthe energy is being delivered, and controlling the delivering of theenergy in response to the monitored temperature.
 13. The method of claim11, wherein a passageway extends through at least a portion of theelectrosurgical ablation probe, the passageway being configured tocirculate the cooling fluid to cool at least portions of the firstelectrode and the second electrode.
 14. The method of claim 13, whereinthe closed distal end portion of the electrosurgical ablation probe isformed at least in part by the inner conductor.
 15. The method of claim13, wherein the first electrode is closer to the distal end of theelectrosurgical ablation probe than the second electrode.
 16. The methodof claim 13, wherein the delivered energy is radiofrequency energy, andfurther comprising maintaining a temperature of the portion of the boneat between about 40 degrees and about 100 degrees Celsius using theradiofrequency energy.
 17. A method of lesioning in a bone of a patientusing an electrosurgical probe, the method comprising: positioning anintroducer assembly into the patient; inserting at least a portion ofthe electrosurgical ablation probe through the introducer assembly andinto the patient; positioning a distal end of the electrosurgicalablation probe adjacent a portion of the bone; supplying energy from anelectrosurgical generator to a first electrode positioned at the distalend of the electrosurgical ablation probe via an inner conductor;delivering energy between the first electrode and a second electrodespaced apart and electrically isolated from the first electrode, and tothe portion of the bone to create a lesion; and circulating a coolingfluid within the electrosurgical ablation probe to cool the firstelectrode and the second electrode; wherein the first electrode isformed from a closed distal end portion of the electrosurgical ablationprobe, and the cooling fluid is circulated within at least a portion ofthe closed distal end portion.
 18. The method of claim 17, furthercomprising monitoring a temperature of the portion of the bone to whichthe energy is being delivered, and controlling the delivering of theenergy in response to the monitored temperature.
 19. The method of claim17, wherein the closed distal end portion of the electrosurgical probeis formed at least in part by the inner conductor.
 20. The method ofclaim 17, wherein the first electrode is closer to the distal end of theelectrosurgical probe than the second electrode.